U.S. patent application number 13/591427 was filed with the patent office on 2014-02-27 for active ionization control with interleaved sampling and neutralization.
This patent application is currently assigned to ILLINOIS TOOL WORKS INC.. The applicant listed for this patent is Manuel C. BLANCO, John A. GORCZYCA, Steven J. MANDRACHIA. Invention is credited to Manuel C. BLANCO, John A. GORCZYCA, Steven J. MANDRACHIA.
Application Number | 20140054470 13/591427 |
Document ID | / |
Family ID | 49118787 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140054470 |
Kind Code |
A1 |
GORCZYCA; John A. ; et
al. |
February 27, 2014 |
ACTIVE IONIZATION CONTROL WITH INTERLEAVED SAMPLING AND
NEUTRALIZATION
Abstract
A method for optimizing performance of a static neutralizing
power supply coupled to a controller and configured to provide an
output to at least one ionizer includes, (a) during a first time
period, sensing a current flow to the at least one ionizer, and (b)
comparing, in the controller, an expected current flow to the
sensed current flow. A difference between the expected and sensed
current flows is proportional to a charge on an object to be
neutralized proximate the at least one ionizer. The method further
includes (c) adjusting, by the controller and based on the
comparison, one or more properties of the output to the at least
one ionizer to neutralize the charge on the object during a second
time period following the first time period, and (d) periodically
repeating steps (a)-(c) for successive first and second time
periods.
Inventors: |
GORCZYCA; John A.;
(Lansdale, PA) ; BLANCO; Manuel C.; (Hillsborough,
NJ) ; MANDRACHIA; Steven J.; (Eagleville,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GORCZYCA; John A.
BLANCO; Manuel C.
MANDRACHIA; Steven J. |
Lansdale
Hillsborough
Eagleville |
PA
NJ
PA |
US
US
US |
|
|
Assignee: |
ILLINOIS TOOL WORKS INC.
Glenview
IL
|
Family ID: |
49118787 |
Appl. No.: |
13/591427 |
Filed: |
August 22, 2012 |
Current U.S.
Class: |
250/424 ;
250/423R |
Current CPC
Class: |
H01T 23/00 20130101 |
Class at
Publication: |
250/424 ;
250/423.R |
International
Class: |
H01J 27/02 20060101
H01J027/02 |
Claims
1. A method for optimizing performance of a static neutralizing
power supply coupled to a controller and configured to provide an
output to at least one ionizer, the power supply having a first
operating state such that one or more properties of the output are
set to fixed baseline levels, and a second operating state such
that the one or more properties of the output are set to
neutralizing levels, the fixed baseline level for at least one of
the one or more properties being different than the neutralizing
level for the at least one of the one or more properties, the
controller being configured to switch the power supply between the
first and second operating states during a sequence of a plurality
of alternating first and second time periods, the method
comprising: (a) during the first time period, sensing a current
flow to the at least one ionizer with the power supply set to the
first operating state; (b) comparing, in the controller, an
expected current flow in the first operating state to the sensed
current flow, wherein a difference between the expected and sensed
current flows is proportional to a charge on an object to be
neutralized proximate the at least one ionizer; (c) based on the
comparison, adjusting, by the controller, at least one of the
neutralizing levels for the one or more properties of the output of
the power supply in the second operating state, wherein adjustments
are made only in response to comparisons with current flows sensed
in the first time period; (d) applying, during the immediately
succeeding second time period, the adjusted neutralizing levels for
the one or more properties of the output of the power supply in the
second operating state to neutralize the charge on the object; and
(e) repeating steps (a)-(d) for successive pairs of the first and
second time periods.
2. The method of claim 1, wherein the at least one ionizer includes
at least one positive ionizer and at least one negative
ionizer.
3. The method of claim 2, wherein the sensed current flow is a net
of current flow to the at least one positive ionizer and current
flow to the at least one negative ionizer.
4. The method of claim 3, wherein the one or more properties of the
output includes a first amplitude applied to the at least one
positive ionizer, a second amplitude applied to the at least one
negative ionizer, and a duty cycle, wherein the fixed baseline
level for each of the first and second amplitudes is between about
4 kV to about 20 kV, and wherein the fixed baseline level for the
duty cycle is 50/50.
5. The method of claim 4, further comprising: (f) during the first
time period, summing the current flow to the at least one positive
ionizer and the current flow to the at least one negative ionizer
to determine a current magnitude with the power supply set to the
first operating state; (g) comparing the current magnitude to
calibration data to determine difference values, the calibration
data having been obtained with the output of the power supply being
set at the fixed baseline levels for the first and second
amplitudes and the 50/50 duty cycle; and (h) using the difference
values to determine a relative condition of the at least one
positive ionizer and the at least one negative ionizer.
6. The method of claim 3, wherein the fixed baseline levels for the
first and second amplitudes are both equal to 0.
7. The method of claim 4, wherein the adjustment to the at least
one of the neutralizing levels includes an adjustment to the
neutralizing level of at least one of the first amplitude, the
second amplitude, or the duty cycle of the output.
8. The method of claim 2, wherein during each first time period,
the sensed current flow is the current flow to one of the at least
one positive ionizer and the at least one negative ionizer.
9. The method of claim 8, wherein the adjustment to the at least
one neutralizing level only affects the output to the other of the
at least one positive ionizer and the at least one negative
ionizer.
10. The method of claim 2, wherein during both of the first and
second time periods the output to each of the at least one positive
and negative ionizers is a uni-polar DC signal.
11. The method of claim 1, wherein a ratio of a length of the
second time period to a length of the first time period is about
10:1.
12. A method for optimizing performance of a static neutralizing
power supply coupled to a controller and configured to provide a
first output having a first amplitude to at least one positive
ionizer and a second output having a second amplitude to at least
one negative ionizer, the power supply having a first operating
state such that one or more of the first amplitude, the second
amplitude, or a duty cycle of the first and second outputs are set
to fixed baseline levels, and a second operating state such that
the one or more of the first amplitude, the second amplitude, or
the duty cycle are set to neutralizing levels, the fixed baseline
level for at least one of the first amplitude, the second
amplitude, or the duty cycle being different than the neutralizing
level for the at least one of the first amplitude, the second
amplitude, or the duty cycle, the controller being configured to
switch the power supply between the first and second operating
states during a sequence of a plurality of alternating first and
second time periods, the method comprising: (a) during the first
time period, sensing a first current flow to the at least one
positive ionizer and a second current flow to the at least one
negative ionizer with the power supply set to the first operating
state; (b) determining a net current flow from the first and second
current flows; (c) comparing, in the controller, an expected net
current flow in the first operating state to the determined net
current flow, wherein a difference between the expected and sensed
current flows is proportional to a charge on an object to be
neutralized proximate the at least one positive ionizer and the at
least one negative ionizer; (d) based on the comparison, adjusting,
by the controller, at least one of the neutralizing levels for the
duty cycle, the first amplitude, or the second amplitude provided
by the power supply in the second operating state, wherein
adjustments are made only in response to comparisons with the net
current flow determined in the first time period; (e) applying,
during the immediately succeeding second time period, the at least
one of the adjusted neutralizing levels for the duty cycle, the
first amplitude, or the second amplitude in the second operating
state to neutralize the charge on the object; and (f) repeating
steps (a)-(e) for successive pairs of the first and second time
periods.
13. A static neutralizing apparatus comprising: (a) a power supply;
(b) at least one ionizer coupled to the power supply and receiving
an output therefrom, the power supply having a first operating
state such that one or more properties of the output are set to
fixed baseline levels, and a second operating state such that the
one or more properties of the output are set to neutralizing
levels, the fixed baseline level for at least one of the one or
more properties of the output being different than the neutralizing
level for the at least one of the one or more properties; and (c) a
controller coupled to the power supply to control the output to the
at least one ionizer, the controller being configured to: (i)
switch the power supply between the first and second states during
a sequence of a plurality of alternating first and second time
periods, (ii) during the first time period, sense a current flow to
the at least one ionizer with the power supply set to the first
operating state, (iii) compare an expected current flow in the
first operating state to the sensed current flow, wherein a
difference between the expected and sensed current flows is
proportional to a charge on an object to be neutralized proximate
the at least one ionizer, (iv) based on the comparison, adjust at
least one of the neutralizing levels for the one or more properties
of the output of the power supply in the second operating state,
wherein adjustments are made only in response to comparisons with
current flows sensed in the first time period, (v) apply, during
the immediately succeeding second time period, the adjusted
neutralizing levels for the one or more properties of the output of
the power supply in the second operating state to neutralize the
charge on the object, and (vi) periodically repeat steps (ii)-(v)
for successive pairs of the first and second time periods.
14. The apparatus of claim 13, wherein the at least one ionizer
includes at least one positive ionizer and at least one negative
ionizer.
15. The apparatus of claim 14, further comprising a memory in
communication with the controller.
16. The apparatus of claim 15, wherein the memory is configured to
store calibration data for determining a performance of the at
least one positive ionizer and the at least one negative ionizer,
the controller being further configured to: (vii) during the first
time period, sum the current flow to the at least one positive
ionizer and the current flow to the at least one negative ionizer
to determine a current magnitude with the power supply set to the
first operating state; (viii) compare the current magnitude to the
calibration data to determine difference values; and (ix) use the
difference values to determine a relative condition of the at least
one positive ionizer and the at least one negative ionizer.
17. The apparatus of claim 14, wherein the one or more properties
of the output includes a first amplitude applied to the at least
one positive ionizer, a second amplitude applied to the at least
one negative ionizer, and a duty cycle, wherein each the fixed
baseline level for each of the first and second amplitudes is
between about 4 kV to about 20 kV, and wherein the fixed baseline
level for the duty cycle is 50/50.
18. The apparatus of claim 13, wherein the power supply, at least
one ionizer, and controller are disposed within a common
housing.
19. The apparatus of claim 13, wherein the controller and the power
supply are housed separately from the at least one ionizer and the
power supply is coupled to the at least one ionizer by a high
voltage cable.
20. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] Embodiments of the present invention are directed to a
neutralization system, and more particularly, to a neutralization
system with interleaved periods of sampling and neutralization to
optimize neutralization of a target object.
[0002] Air ionization is an effective method of eliminating static
charges on target surfaces. Air ionizers generate large quantities
of positive and negative ions in the surrounding atmosphere that
serve as mobile carriers of charge in the air. As ions flow through
the air, they are attracted to oppositely charged particles and
surfaces. Neutralization of electrostatically charged surfaces can
be rapidly achieved through this process.
[0003] Air ionization may be performed using electrical ionizers,
which generate ions in a process known as corona discharge.
Electrical ionizers generate air ions by intensifying an electric
field around a sharp point until the field overcomes the dielectric
strength of the surrounding air. Negative corona discharge occurs
when electrons are flowing from the electrode into the surrounding
air. Positive corona discharge occurs as a result of the flow of
electrons from the air molecules into the electrode.
[0004] Ionizer devices, such as an alternating current (AC) or
direct current (DC) charge neutralizing system, take many forms,
such as ionizing bars, air ionization blowers, air ionization
nozzles, and the like, and are utilized to neutralize static
electrical charge by emitting positive and negative ions into the
workspace or onto the surface of an area. Ionizing bars are
typically used in continuous web operations such as paper printing,
polymeric sheet material, or plastic bag fabrication. Air
ionization blower and nozzles are typically used in workspaces for
assembling electronics equipment such as hard disk drives,
integrated circuits, and the like, that are sensitive to
electrostatic discharge (ESD).
[0005] Neutralization output can be adjusted in response to the
determination of charge on the target object. FIG. 1 is a schematic
block diagram of an exemplary prior art neutralization system 10. A
target, such as a moving web 12 having an undesirable charge
thereon is passed by an ionizer bar 14 with ionizers, such as pins,
generating positive and negative ions. Downstream of the ionizer
bar 14 is an external sensor 16 that detects a residual charge on
the moving web 12. Data from the sensor 16 is passed into a
controller 20 disposed within a housing 18 and coupled to one or
more high voltage power supplies 22a, 22b, which are in turn
coupled to the ionizer bar 14. Based on the sensor data, the
controller 20 generates and outputs signals representing
adjustments necessary to the output of the high voltage power
supplies 22a, 22b in order to optimize neutralization on the target
web 12. The high voltage power supplies 22a, 22b are coupled to the
ionizer bar 14 by one or more high voltage cables 24.
[0006] The use of a downstream sensor has significant drawbacks,
such as the need for additional costly equipment and connecting
cables that may be too large or awkward to practically place into
the workspace. Some sensors may also not be approved for placement
in hazardous locations (e.g., areas at risk of fire or explosion
hazards).
[0007] In addition, over time, an ionizer may accumulate debris. In
order to maintain optimal performance of the ionizer, it is
necessary to clean the ionizer in order to remove the debris. As an
ionizer accumulates debris, the ionizer's charge will decrease and,
therefore, the current flowing from the voltage supply into the
ionizer will also decrease. A method for having the ionization
self-calibrate and indicate performance is described in U.S. Pat.
No. 8,039,789, the entire contents of which are incorporated by
reference herein. However, the method requires the initial
accumulation of calibration data for a plurality of operating
states of the high voltage power supply. Real-time data, in
particular a sum of the current output to the positive and negative
ionizers, acquired during operation is then compared to the closest
data point to determine a difference in performance. The
accumulation of calibration data for what may be 250 or more data
points can be time consuming, and requires a large memory space to
store the necessary baseline table.
[0008] It is desirable to provide a static neutralization system
that can optimize neutralization of a target object without the
need for an external downstream sensor.
BRIEF SUMMARY OF THE INVENTION
[0009] Briefly stated, an embodiment of the present invention
comprises a method for optimizing performance of a static
neutralizing power supply coupled to a controller and configured to
provide an output to at least one ionizer. The method includes, (a)
during a first time period, sensing a current flow to the at least
one ionizer, and (b) comparing, in the controller, an expected
current flow to the sensed current flow. A difference between the
expected and sensed current flows is proportional to a charge on an
object to be neutralized proximate the at least one ionizer. The
method further includes (c) adjusting, by the controller and based
on the comparison, one or more properties of the output to the at
least one ionizer to neutralize the charge on the object during a
second time period following the first time period, and (d)
periodically repeating steps (a)-(c) for successive first and
second time periods.
[0010] Another embodiment of the present invention comprises a
method for optimizing performance of a static neutralizing power
supply coupled to a controller and configured to provide a first
output to at least one positive ionizer and a second output to at
least one negative ionizer. The method includes (a) during a first
time period, sensing a first current flow to the at least one
positive ionizer and a second current flow to the at least one
negative ionizer, (b) determining a net current flow from the first
and second current flows, and (c) comparing, in the controller, an
expected net current flow to the determined net current flow. A
difference between the expected and sensed current flows is
proportional to a charge on an object to be neutralized proximate
the at least one positive ionizer and the at least one negative
ionizer. The method further includes (d) adjusting, by the
controller and based on the comparison, at least one of a duty
cycle or amplitude of at least one of the first and second outputs
provided by the power supply to neutralize the charge on the object
during a second time period following the first time period, and
(e) periodically repeating steps (a)-(d) for successive first and
second time periods.
[0011] Yet another embodiment of the present invention comprises a
static neutralizing apparatus including a power supply, at least
one ionizer coupled to the power supply and receiving an output
therefrom, and a controller coupled to the power supply to control
the output to the at least one ionizer. The controller is
configured to (i) during a first time period, sense a current flow
to the at least one ionizer, and (ii) compare an expected current
flow to the sensed current flow. A difference between the expected
and sensed current flows is proportional to a charge on an object
to be neutralized proximate the at least one ionizer. The
controller is further configured to (iii) adjust, based on the
comparison, one or more properties of the output to the at least
one ionizer to neutralize the charge on the object during a second
time period following the first time period, and (iv) periodically
repeat steps (i)-(iii) for successive first and second time
periods.
[0012] Still another embodiment of the present invention comprises
a method for optimizing performance of a static neutralizing power
supply coupled to a controller and configured to provide an output
to at least one ionizer. The method includes placing the power
supply in a calibration mode, stepping the power supply through one
or more of a range of adjustments, collecting expected current flow
values at each step and storing the calibration data in a memory,
placing the power supply in an operating mode, sensing a real-time
current flow to the at least one ionizer, comparing, in the
controller, the sensed real-time current flow to the one of the
expected current flow values and determining difference values
therebetween, and using the difference values to adjust, by the
controller, one or more properties of the output to the at least
one ionizer to restore the real-time current flow to one of the
expected current flow values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing summary, as well as the following detailed
description of preferred embodiments of the invention, will be
better understood when read in conjunction with the appended
drawings. For the purpose of illustration, there is shown in the
drawings an embodiment which is presently preferred. It should be
understood, however, that the invention is not limited to the
precise arrangements and instrumentalities shown.
[0014] FIG. 1 is a schematic block diagram of a prior art
ionization system;
[0015] FIG. 2 is a schematic block diagram of an ionization system
in accordance with a preferred embodiment of the present
invention;
[0016] FIG. 3 is a timeline showing alternating and repeating time
periods for use in accordance with preferred embodiments of the
present invention;
[0017] FIG. 4 is a flowchart of a process for sensing target object
charge and adjusting neutralization settings in accordance with
preferred embodiments of the present invention; and
[0018] FIG. 5 is a flowchart associated with the collection of real
time sampling and comparison process with set point adjustments of
an ionization system in accordance with a preferred embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Certain terminology is used in the following description for
convenience only and is not limiting. Additionally, the words "a"
and "an", as used in the claims and in the corresponding portions
of the specification, mean "at least one." In the drawings, the
same reference numerals indicate like elements throughout.
[0020] Referring to FIG. 2, a first preferred embodiment of a
neutralization system 110 is shown. A controller, processor, or
other controlling circuitry 120 or processor 120 (for simplicity,
hereinafter referred to as "controller 120") preferably controls
the functionality of the neutralization system 110. The controller
120 may accept input directly from a user 130, a computer interface
132 coupled to an external computer (not shown), or the like.
Various high voltage generating topologies can be used in the
preferred embodiments of the present invention. In particular,
various controllers 120, such as microcontrollers or
microprocessors, can be used in the application of the preferred
embodiments of the present invention. One suitable controller 120
is the commercially available Z8 Encore microprocessor manufactured
by Zilog, Inc. The controller 120 is also preferably further in
communication with a memory 121, which can be any known or suitable
memory device such as random access memory (RAM), read only memory
(ROM), flash RAM, hard disk, optical disk, or the like.
[0021] The controller 120 is coupled to one or more high voltage
(HV) power supplies 122a, 122b, and preferably a positive HV power
supply 122a and a negative HV power supply 122b. However, other HV
power supplies, such an alternating current (AC) power supply, may
also be used in accordance with the invention. The HV power
supplies 122a, 122b supply power to an ionization emitter 114,
shown in FIG. 2 as an ionizer bar 114. In a preferred embodiment,
the ionizer bar 114 includes one or more ionizing pins 114a
associated with the positive HV power supply 122a and a
corresponding number of ionizing pins 114b associated with the
negative HV power supply 122b. In other embodiments, one or pins
may be alternately connected to positive and negative outputs by
switches or the like, or to an AC HV power supply. In embodiments
with a single direct current (DC) HV power supply, the ionizing
pins of the ionizer bar 114 would receive only one polarity. The
controller 120 controls the output of the HV power supplies 122a,
122b to the ionizer bar 114.
[0022] In a preferred embodiment, the controller 120, the HV power
supplies 122a, 122b, and the ionizer bar 114 are disposed within a
common housing 118. This eliminates the need for high voltage
cables to connect the ionizer bar 114 to the power supplies 122a,
122b and provides a more efficiently sized neutralization system
110. However, embodiments of the present invention may be used with
other configurations, such as, for example, the configuration shown
in FIG. 1 where the ionizer bar 114 would be located externally
from the HV power supplies 122a, 122b.
[0023] In the present embodiment shown in FIG. 2, the external
sensor 16 in FIG. 1 is no longer necessary for determining the
residual charge on the target 112. Rather, the determinations for
adjustments to the output signals from the HV power supplies 122a,
122b will be described in detail below.
[0024] Embodiments of the present invention effectively use the
ionizer bar 114 as the sensor for determining the charge on the
target object 112. When the target object 112 bears a charge of a
certain threshold, current flow at the pins 114a, 114b of the
ionizer bar 114 may be induced or suppressed, based on the polarity
of the charge on the target object 112. A difference between an
expected current flow and the actual current flow is proportional
to the charge on the target object 112, and can therefore be used
to adjust the operational settings of the neutralization system 110
to better neutralize the target object 112. One method of measuring
current flow at the pins 114a, 114b is described in U.S. Pat. Nos.
6,130,815 and 6,259,591, the entire contents of both of which are
incorporated by reference herein.
[0025] For example, the net neutralization current output
I.sub.neut at the ionizer pins 114a, 114b of the ionizer bar can be
determined by the following equation:
I.sub.neut=I.sup.+-I.sup.--I.sub.0
where I.sup.+ is the absolute value of the output current at the
positive ionizer pins 114a, I.sup.- is the absolute value of the
output current at the negative ionizer pins 114b, and I.sub.0 is a
neutralization current present at time t=0, essentially a
correction factor, which ideally would be equal to zero. The net
neutralization output current I.sub.neut is proportional to charge
on the target object 112, speed of the target object 112, and
distance of the pins 114a, 114b from the target object 112. If
there is insufficient charge on the target object 112 to induce or
suppress current at the ionizer bar 114, then in most cases the net
neutralization output current I.sub.neut would be zero. If
I.sub.neut>0, then the charge on the target object 112 is
negative, indicating that more positive net charge is required to
be output by the ionizer bar. If, on the other hand,
I.sub.neut<0, then the charge on the target object 112 is
positive, and more negative net charge must be output to neutralize
the target object 112.
[0026] It should be further noted that a normalized net current
value I.sub.norm can be used to correct for effects caused by the
length of the ionizer bar 114. The normalized net current is given
by the equation:
I.sub.norm=I.sub.neut/I.sub.mag
where I.sub.mag represents the magnitude of the neutralization
current, which is given by the equation:
I.sub.mag=I.sup.++I.sup.-
[0027] According to embodiments of the present invention, these
concepts are utilized by interleaving periods of sampling at the
ionizer bar 114 with periods of normal operation for neutralizing
the target object 112. For example, FIG. 3 shows a timeline 200 of
operation of the neutralization system 110, which includes
alternating periods of normal operation 202, wherein the
neutralization system 110 is operating under normal conditions to
neutralize charge on the target object 112, with sampling periods
204, during which data is collected by the controller 120 to
determine whether adjustments to the operating conditions during
the operation period 202 are necessary. It is preferred that the
length and frequency of the sampling periods 204 is kept to a
minimum, as often the neutralizing capabilities of the system 10
are compromised during the sampling period 204. However, this must
be balanced against the need to monitor changes in the charge level
of the target object 112, which can vary greatly over time. It is
preferred that a ratio of the normal operating periods 202 to the
sampling periods 204 is about 10:1, although other ratios are
contemplated as well.
[0028] FIG. 4 is a flow chart of an exemplary method 300 performed
by the controller 120 in accordance with preferred embodiments of
the present invention. Upon entering a sampling period 204, the one
or more power supplies 122a, 122b are set to sensing levels (step
302). For example, typically the output to the ionizer bar 114 is a
waveform having a duty cycle, amplitude, frequency, and the like.
However, in certain embodiments, the output to the respective
ionizing pins 114a, 114b may be uni-polar DC signals, in which case
both the positive and negative HV power supplies 122a, 122b are
constantly on, rather than pulsing. The controller 120 may set the
amplitude of the output of the positive and negative HV power
supplies 122a, 122b to a nominal level, for example between about 4
kV to about 20 kV. The duty cycle (i.e., the ratio of positive to
negative ion generation during a cycle of the waveform) is also
preferably set to 50/50. The frequency and/or other characteristics
of the waveform can also be set to nominal levels during the
sampling period 204. By maintaining nominal voltage levels at the
ionizing pins 114a, 114b during the sampling period 204, the
neutralization system 110 can continue to neutralize charge on the
target object 112 during the sampling period, with the
effectiveness of an open-loop system.
[0029] In an alternative embodiment, the step of setting the output
to sensing levels 302 may include shutting down the voltage output
to the ionizer bar 114 from the power supplies 122a, 122. For
example, the power supplies 122a, 122b may be placed into a mode or
set to a set point such that no signal is output to the ionizer bar
114a (e.g., Vprog=0). As a result, the ionizing pins 114a, 114b are
not held at any voltage, and current generated at the pins 114a,
114b is purely the result of charge on the target object 112.
[0030] At step 304, current to the ionizing pins 114a, 114b is
sensed by the controller 120. At step 306, the sensed current is
compared to the expected current flow based on the sensing levels,
which should typically be zero as described above. Once again, the
difference in expected and sensed current flows is proportional to
the charge on the target object 112 passing proximate the ionizer
bar 114.
[0031] Based on the comparison, at step 308, the controller 120
determines whether the properties (e.g., amplitude, duty cycle,
frequency, or the like) of the output during the normal operation
periods 202 are sufficient to neutralize the charge detected on the
target object 112. If not, the controller 120 proceeds to step 310,
where one or more of the properties are adjusted to levels that
will more effectively neutralize the detected charge. Once the
properties are adjusted, the output is set to the adjusted
operating levels and applied for the duration of the normal
operation period (step 312). It should be noted that the
adjustments in step 310 can be made during the sampling period 204,
during the normal operation period 202, or between the two periods
202, 204. If the determination is made at step 310 that the current
neutralization settings are sufficient for neutralizing the
detected charge on the target object 112, then step 310 is skipped
and the controller proceeds directly to step 312. Upon entry of the
next sampling period 204, the method 300 is repeated.
[0032] In another embodiment, at step 304, only the unwanted
polarity of the output from the power supplies 122a, 122b is
measured, while the other polarity is optimized based on the
measurements of the unwanted polarity. That is, rather than basing
output adjustments on a net neutralization current (I.sub.neut) of
the power supplies 122a, 122b, the sensed current is the current
flow to either the positive ionizing pins 114a or the negative
ionizing pins 114b, and the adjustments are made to the output of
the other of the positive or negative ionizing pins 114a, 114b
based on the suppression of current at the unwanted polarity. For
example, if the charge on the target 112 is primarily negative,
then during the sampling period 204, the suppression of current at
the negative ionizing pins 114b is measured, and the magnitude of
the suppression can be used to adjust the properties of the output,
particularly at the positive ionizing pins 114a. This procedure
similarly works for a positively charged target 112 by measuring
current suppression to the positive ionizing pins 114a while
adjusting the output of the negative HV power supply 122b to
optimize neutralization. In this way, the sampling period 204 can
occur on the portion of the duty cycle where the unwanted polarity
is being applied, and the operating period 202 occurs on the
remainder of the cycle where the desired polarity is being
applied.
[0033] In another embodiment, during both the normal operation
period 202 and the sampling period 204, both of the HV power
supplies 122a, 122b output uni-polar DC signals to the respective
ionizing pins 114a, 114b. As current changes are observed during
the sampling period 204, the amplitude on the required polarity is
adjusted incrementally. At some point, the current will saturate.
Upon saturation, or a percentage thereof, there is enough voltage
present on the respective ionizing pins 114a, 114b to deplete the
charge on the target object 112. It should be noted that this
voltage may be lower than the requirement for ionization because of
field-induced current flow.
[0034] The techniques described above are merely exemplary, and
other methods for establishing an expected current and determining
actual current using the ionizer bar 114 may be used in keeping
with the invention. It should be noted that for the methods
described above, speed of the target object 112 and distance of the
ionizer bar 114 from the target object 112 are two factors which
may affect the calculations in converting the sensed current levels
to power supply output information. Accordingly, a gain term may be
applied that scales the translation accordingly. The gain term may
be a positive or negative value. For example, a greater distance
between the ionizer bar 114 and the target object 112 requires a
higher gain term, while a close distance of the ionizer bar 114 to
the target object 112 may result in over-compensation and require a
negative gain term as an offset.
[0035] FIG. 5 is a flowchart associated with the collection of real
time sampling and comparison process with set point adjustments of
an ionization system to determine the relative condition of the of
the ionizer bar 114. The controller 120 regularly samples (step
402) the neutralization current magnitude (I.sub.mag), which may be
calculated as described above. Previously determined calibration
data is retrieved from memory 121 (step 404) for the set point. An
absolute percentage difference is calculated (step 406) from the
stored value and the real time reading. In a preferred embodiment
the calculation used to determine the difference is:
I.sub.D=[I.sub.cal-I.sub.mag]
where I.sub.D is the absolute value of base line calibration
measurement (I.sub.cal) minus the real-time measurement
(I.sub.mag). The retrieved I.sub.cal is assigned a value of 100%.
An error from the 100% is calculated (step 408). The percentage
difference E % from the baseline calibration is calculated by the
following equation:
E %=100*(1-(I.sub.D/I.sub.cal)
[0036] Upon calculation of the percentage difference, the meter or
display of the neutralization system 110 is updated (step 410) to
indicate operating conditions of the ionizer bar 114. The
percentage difference E % is compared against threshold limits for
the ionizer bar selected (step 412). A clean bar indicator (not
shown) is illuminated when the threshold limit is exceeded (step
414). The threshold for the limit wherein the ionizer bar should be
cleaned can be configured by the user, a sensor, a microprocessor,
or set by software coupled to or located within the controller 120.
Other main loop processes (step 416), including the determination
of the neutralization current during the sampling period 204 (step
418) and adjustment of the operating set point (step 420) occur as
well.
[0037] Use of the sampling period 204 can also aid in making the
self-calibration and performance indication of the neutralization
system more efficient. In accordance with a preferred embodiment of
the present invention, the current magnitude I.sub.mag is
determined by the controller 120 during the sampling period 204
(i.e., in step 418). Thus, the calibration set point is preferably
identical to the sensing levels described above (e.g., nominal
amplitude and 50/50 duty cycle or the like). By determining the
neutralization current magnitude based on the sensing levels during
the sampling period 204, the results can be compared to a single
data point, rather than to hundreds of set points. Steps 402 and
404 in FIG. 5 would thereby be eliminated. In addition, such a
method would remove the need for obtaining calibration data for
hundreds of baseline values at the start of operation. However, it
is contemplated that other conventional methods for determining
error and operating condition in the neutralization system 110 can
be used as well.
[0038] In an alternative embodiment, current sensing may be
performed with much greater frequency and at operating output
levels. FIG. 6 is a flow chart for an exemplary method 500 of such
an embodiment. It should be noted that this method requires
collection of calibration data, specifically current flows, for the
possible operating set points of the neutralization system 110. A
method for collecting calibration data is described below with
reference to FIG. 7. Referring to FIG. 6, at step 502, while the HV
power supplies 122a, 122b are outputting signals at operating
levels to the respective ionizing pins 114a, 114b, current output
is detected. At step 304, the calibration point closest to the
present operating level of the neutralization system 110 is
determined. At step 506, the data from the determined calibration
point is retrieved from memory 121. The order of steps 502, 504,
and 506 in FIG. 6 is exemplary only, and may occur in different
order, such as retrieval of the calibration data prior to sensing
of the immediate current flow.
[0039] At step 508, the sensed current is compared to the expected
current based on the calibration data. At step 510, a determination
is made as to whether an adjustment to one or more properties of
the output from the HV power supplies 122a, 122b is necessary to
optimize neutralization of the target 112. If so, such adjustments
are made at step 512 and applied at step 514. If not, the
controller 120 skips step 512 and continues applying (step 514) the
present output. The method 500 is repeated as needed.
[0040] FIG. 7 is a flowchart illustrating a method 600 for the
collection of the calibration data. In the example shown in the
flowchart, a calibration button of the neutralization system 110 is
pushed (step 602) to enter a calibration mode. Thereafter, a
calibration module or sequence 604 is started. During this
sequence, a plurality of baseline output currents of the ionizer
are measured at one or more points of the HV power supplies 122a,
122b to the ionizer bar 114. These output measurements are compiled
as the baseline calibration data at each of the points measured.
The set points in memory cover all setting ranges, preferably by
uniformly dividing the range and determining the set points. In one
embodiment, 250 set points may be stored in the memory 121 for
compiling the baseline currents data. The baseline currents are
measured and stored at each point (step 606).
[0041] In a preferred embodiment, the calibration sequence is
started (step 604), and the output current of the ionizer at a
plurality of points is measured and stored at each point. The set
points are retrievable from the memory 121 or from another input
source (step 608). The set points cover all setting ranges. To
cover all setting ranges, the range is uniformly divided and the
set points are determined. In a preferred embodiment, a range of
100-300 set points are measured and stored, as a set point array
(step 610). In a more preferred embodiment, 250 set points are
measured and stored. The HV power supplies 122a, 122b are set to
each of the points (step 612) and the current data is sampled at
each of the points (step 614). When there is no more set points to
implement (step 616), and the data is collected at each of the
points, the calibration data is stored (step 606). In other
preferred embodiments, the data is stored throughout the collection
process. During this calibration the output values of the current
are reset to the baseline values for the ionizer bar 114a (step
618). The HV power supplies 122a, 122b then return to normal
operation (step 620).
[0042] From the foregoing, it can be seen that embodiments of the
present invention comprise a method and apparatus for optimizing
neutralization of a target object. It will be appreciated by those
skilled in the art that changes could be made to the embodiments
described above without departing from the broad inventive concept
thereof. It is understood, therefore, that this invention is not
limited to the particular embodiments disclosed, but it is intended
to cover modifications within the spirit and scope of the present
invention as defined by the appended claims.
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